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  Satellite Images of Environmental Change: Imperial Valley 1973 to 1992
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downImperial Valley, California
down arrowThe river and the sink
down arrowChanges 1973 to 1992

  Imperial Valley, California 
  The Landsat images below show the Imperial Valley, on the border of California and Mexico.

This valley, also known as the Salton Sink, the Salton Basin, and the Salton Trough, is actually an extension of the Gulf of California, cut off from the Gulf by the Colorado River's delta fan. The valley was renamed Imperial by turn-of-the-century land investors.1 The area south of the border is known as the Mexicali Valley.

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  Landsat image or map to canal gate photograph Salton City photograph Landsat 1  1973 tab Landsat 4 1992 tab international map of the world 1947 legend
  Several cities are visible within the area of irrigated agriculture in the valley, which is surrounded by the natural desert. At the bottom of the sink lies the Salton Sea, the largest lake in California. It lacks an outlet to the ocean, or rather the ocean lacks an outlet to it, since the valley lies below sea level.
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  The river and the sink
  For thousands of years, the Colorado River flowed by the valley, above and to the east, on its way to the nearby Gulf of California. The river was higher than the valley, but it was hemmed in by its own natural "levees", land barriers on either bank built up over the years from the silt left behind by floods. With each flood these "levees" grew a bit higher and harder to break through. But once in a while the Colorado would break out and pour down into the Salton Sink, partly filling it. Then the break would fill with silt, the river would revert to its normal channel, and the basin would dry up again.

map showing the relationship between the Salton Sea, Colorado River and the Gulf of California
The Salton Sea was formed in 1905 when the Colorado River Flooded.
National Atlas of the United States®

European American settlers saw that the Imperial Valley had good soils for agriculture, except for being extremely dry. In 1901 a company began diverting some Colorado River water down into the valley for irrigation, imitating what the Colorado had done naturally thousands of times. In 1905 the company lost control; during a flood the Colorado broke through the half-finished headgate of an irrigation ditch. The river kept widening the ditch, until almost the entire river was flowing into the sink rather than toward the Gulf of California. It took engineers and work crews until 1907 to return the river to its proper course, by which time a considerable lake had formed.2

Ironically, what happened as an uncontrolled accident in 1905 was later accomplished deliberately. Data from 1961-1963 indicate that where the All-American Canal (visible just north of the border) tapped into the Colorado, it carried 90% of the river's water away to the valley (5 million acre-feet annually), leaving only a tenth as much to flow toward the Gulf of California.3

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  Changes 1973 to 1992
  The zoom-in images show the growth of El Centro, California, and the urban area of Mexicali/Calexico on the border (see the map below). From 1970 to 1990, these cities' populations grew by the following amounts:

* El Centro: 19,272 to 31,384 (63%)
* Calexico: 10,625 to 18,633 (76%)
* Mexicali: 459,900 to 712,400 (55%)4

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   Landsat image or map photograph of an irrigated field in the Imperial Valley Landsat 1 1973 tab Landsat 4 1992 tab international map of the world 1947 tab legend tabs
  The level of the Salton Sea is now sustained by an inflow of municipal and industrial drainage, as well as agricultural irrigation drainage, all of which flows through some of the old river beds that carried Colorado River overspill. The evaporative concentration of selenium and other salts in this runoff now threatens birds and other wildlife which rely on the Sea. To address this problem, evaporation basins might be built to extract some of the salt. Saltwater pumping to the Gulf of California might also be attempted.
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1 Gordon B. Oakeshott, 1971, California's changing landscapes; a guide to the geology of the state: New York, McGraw-Hill (388 p.), p. 20, 343.
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2 Donald Worster, 1985, Rivers of empire; water, aridity, and the growth of the American West: New York, Pantheon (402 p.), p. 196.
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3 Charles C. McDonald and Omar J. Loeltz, 1976, Water resources of the lower Colorado River - Salton Sea area as of 1971: U.S. Geological Survey Professional Paper 486-A (34 p.), p. A9.
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4 El Centro and Calexico data are U.S. Census figures for "Calexico city" and "El Centro city". Mexicali data is for "Mexicali Conurb.", from the Consortium for International Earth Science Information Network, 1994?, Population data collection for Mexico: Saginaw, Mich., CIESIN.
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Daniel T. MacDougal, 1914, The Salton Sea; a study of the geography, the geology, the floristics, and the ecology of a desert basin: Washington, D. C., Carnegie Institution, 182 p.

C.E. Grunsky, 1907, The lower Colorado River and the Salton Basin: Transactions of the American Society of Civil Engineers, vol. 33, no. 2, February 1907, p. 102-152.

Allen Day, 1906, The inundation of the Salton Basin by the Colorado River and how it was caused: Scientific American, vol. 94, 14 April 1906, p. 310-312.

George Wharton James, 1906, The overflow of the Colorado River and the Salton Sea: Scientific American, vol. 94, 21 April 1906, p. 328-329.

Satellite images
LM1041037007316090 and LM1042037007314390 (Landsat 1 MSS, 9 June / 23 May 1973)
LM4039037009218290 (Landsat 4 MSS, 30 June 1992)

U.S. Geological Survey, 1947 [compiled 1947, engraved and printed 1952], Los Angeles: International Map of the World I-11, scale 1:1,000,000.

Courtesy of the Imperial Irrigation District.




Adapted from Earthshots, 8th ed., 12 January 2001, EROS Data Center. U.S. Geological Survey.

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